1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by irradiating the recording medium with near-field light.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium. The slider has a medium facing surface configured to face the recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end).
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To eliminate this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To resolve the foregoing problems, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Patent Application Publication No. 2007/0139818 A1 discloses a thermally-assisted magnetic recording head configured to excite plasmons on a plasmon generator (a near-field-light generating layer) by directly irradiating the plasmon generator with laser light.
U.S. Pat. No. 8,619,517 B1 discloses a technology in which the surface of the core of the waveguide and the surface of the plasmon generator are arranged to face each other with a gap therebetween, so that evanescent light that occurs from the surface of the core based on the laser light propagating through the core is used to excite surface plasmons on the plasmon generator to generate near-field light based on the excited surface plasmons.
The configuration in which a plasmon generator is directly irradiated with laser light to excite plasmons on the plasmon generator, such as one disclosed in U.S. Patent Application Publication No. 2007/0139818 A1, has a number of problems as follows. First, such a configuration has the problem of low efficiency of transformation of laser light into near-field light because most part of the laser light is reflected at the surface of the plasmon generator or transformed into thermal energy and absorbed by the plasmon generator. Further, the aforementioned configuration has the problem that the plasmon generator greatly increases in temperature when it absorbs thermal energy, and this may result in deformation of or damage to the plasmon generator.
The configuration in which evanescent light is used to excite surface plasmons on a plasmon generator, such as one disclosed in U.S. Pat. No. 8,619,517 B1, provides higher efficiency of transformation of laser light into near-field light when compared with the case of directly irradiating the plasmon generator with laser light.
However, even the configuration in which evanescent light is used to excite surface plasmons on a plasmon generator causes an increase in temperature of the plasmon generator although the increase is smaller than that caused by the configuration in which the plasmon generator is directly irradiated with laser light to excite plasmons on the plasmon generator.
To avoid the problem associated with a temperature increase of the plasmon generator, the power of the laser light can be reduced to allow the plasmon generator to generate a smaller amount of heat. In such a case, however, it is not possible to apply a sufficient amount of heat to the recording medium.